1. Field of the Invention
The present invention generally relates to the technical field of mobile communications, and particularly relates to a data center, cache server, and method for use in a mobile communication system.
2. Description of the Related Art
In the technical field of mobile communications, various services are put into practice as a result of improvements in the performance of mobile terminals such as portable phones. Especially, development in the data delivery service such as music delivery, video delivery, and the like is remarkable. The data delivery service includes a mobile data center type and a data download type, by which users use data downloaded to their user terminals.
In the case of the data download type, delivered data is stored in the terminal device (or in an external memory card or the like attached to the terminal device), so that there is a limit to the size of the data. Further, a problem may arise in that the data may be lost or become in the possession of others due to the loss or failure of the terminal device.
In the case of the mobile-data-center-type service, data delivered to a terminal device is not stored in the terminal device, but is stored in a storage space on the network. In this method, various data including music, video, and private information may be stored on the network. The use of the mobile-data-center-type service offers an advantage in that the data storage size can be significantly increased. Further, the problem of data being lost or becoming in the possession of others due to the loss or failure of the terminal device can be prevented effectively.
The communication speed of portable phones is significantly increasing, and there is also a tendency that the data size of each file will increase. It will become increasingly easier to play data via a network without storing data in the terminal device. It is thus expected that the demand for the mobile-data-center-type service will increase.
When carriers provide mobile-data-center-type services, each carrier needs to store user data. The size of data that needs to be stored will increase as a result of diversification in service type and an increase in the speed and size of communication, which leads to a concern about an increase in the data storage space.
FIG. 1 is a drawing showing a configuration in which a shared storage space (shared disk area) is provided at a data center for a plurality of user apparatuses for the purpose of avoiding such an increase in the data storage space. Data stored in the shared disk area is shared by the plurality of user apparatuses. In the illustrated example, the data contents of “file A” and “file B” are stored in the shared area for terminal apparatus i, ii, and iii, and each terminal has a link file A pointing to the “file A” contents and a link file B pointing to the “file B” contents. With this arrangement, a relatively small storage space is sufficient for the purpose of storing files A, B, and C for the terminal apparatus i, storing files A, B, and E for the terminal apparatus ii, and storing files A, B, and F for the terminal apparatus iii.
Since the data center is situated at a higher level in hierarchy than the radio access network (RAN), there is a risk that the data center may not be able to quickly respond to access from the terminal apparatuses.
Although not specific to mobile communications systems, Patent Document 1 discloses a computer system using a cache hierarchy method in which a reference rate is compared with a threshold to determine whether data should be or should not be stored in cache while ensuring that the same data be not stored in multiple caches. It may be possible to utilize such cache hierarchy in a mobile communication system.
[Patent Document 1] Japanese Patent Application Publication No. 2002-99465
FIG. 2 is a drawing showing a configuration in which a core network CN and a radio access network RAN are each provided with a cache server. In this communication system, storage units are arranged in a descending order of storage capacity as follows: the storage unit of the data center, the cache server of the core network CN, and the cache servers of the radio access network RAN. Further, communication paths are arranged in a descending order of data transfer speed as follows: a communication path A, a communication path B, and a communication path C. In terms of transmission delay with respect to the mobile terminals i and ii, however, RAN, CN, and the data center are arranged in an ascending order. In such system in which a related-art cache system is incorporated, as a general principle, each of the cache memories in hierarchy stores data in the order in which the data is received. Cache efficiency is improved merely by the fact that the duplicate storing of data is avoided to some extent. Depending on the communication state, there may be a situation in which data corresponding to a weak demand for real-time response is stored at a lower level node while data corresponding to a strong demand for real-time response is stored at a higher level node. In this case, the user apparatus needs to go to the length of accessing the higher level node in order to acquire the data corresponding to a strong demand for real-time response. This may undermine the intention to improve data throughput by providing cache memories.
Further, the storage capacity of each cache server provided in the radio access network and the core network is not the same across the board. It is thus difficult to store data in each cache server according to the same decision criteria as was used in the related art.
Accordingly, there is a need to improve data throughput by efficiently utilizing a RAN cache server provided in RAN and a CN cache server provided in CN with respect to a mobile communication system that includes user apparatuses, a radio access network RAN, a core network CN, and a data center connected to the core network.